Can Prototype portal put a Lotus gloom directly into play? And can master transmuter put Lotus bloom directly into play?
You sure can. Neither of these cards cares that Lotus Bloom has no mana cost. Prototype portal will see it's converted mana cost as 0 (for its own ability), and Transmuter just doesn't care about costs at all.
You can also bring them back with {Salvaging Station}.
Thank you for a quick reply!